Unusual and kind of surprising that it relies on a direct-impact rather than timed or proximity fuse, like most AA weapons I know of. I guess its guidance and travel speed must be sufficient to ensure a solid impact anyhow, in which case that warhead sounds deliciously devastating.
I also just realized a moment of fridge brilliance in your design here... Considering that your setting is a moderately advanced sci-fi setting, the armor on the sorts of high-sped vehicles this Tomahawk is designed to engage might well be significantly better than what we can armor modern aircraft with. In that case indirect, shrapnel-based conventional flak weapons might well prove to be rather ineffective, and the Tomahawk's powerful HE/KEP warhead would be just what the doctor ordered.
I originally considered a proximity fuse but then I thought about the guidance being quite advanced, along with larger fins than you might find on real world MANPAD AA missiles to help it better adjust to any evasive movements. As for the dart, I pictured that punching through the blast riddled skin and into something it wouldn't mix well with.